SAN FRANCISCO — The Latest on investigations into several close call incidents at San Francisco International Airport (all times local):

4 p.m.

Aviation experts say San Francisco International Airport is one of the more difficult airports to land planes.

Longtime American Airlines pilot Chris Manno said Wednesday the runways are close together, requiring extra attention when landing.

Aviation consultant John Cox said the airport’s location along the San Francisco Bay as well as the air traffic and overall design adds additional complications.

Federal authorities on Wednesday blamed pilots for three near-accidents during recent landings and are investigating the causes of another. A fifth close call was blamed on traffic control.

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12:30 p.m.

A spokesman for San Francisco International Airport says several safety improvements have been made since December 2016, when a plane almost entered a busy runway.

Airport spokesman Doug Yakel said Wednesday that more lights have been added to the runways; a confusing taxiway has been closed; and a ground radar system has been reinforced to give pilots a greater level of precision when landing.

Last week, the Federal Aviation Administration re-certified the airport after an in-depth review of its operations.

The FAA said in a report that three of the five close-calls involving aircraft reported in the past 16 months at the busy airport were caused by pilots.

In another incident, a plane was mistakenly cleared to land on the wrong runway by a tower controller.

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12:15 a.m.

An Air Canada pilot says he aborted a landing at San Francisco International Airport before hearing from the control tower because “things were not adding up” when the jet nearly landed on a taxiway occupied by four other planes last July.

In a National Transportation Safety Board report posted Wednesday, Capt. Dimitrios Kisses said the airport was dark and the runway “did not look good” when he opted to go around. It says both pilots reported being tired.

The agency said the A320 with 140 people aboard was headed for a taxiway because the pilots had mistaken it for a runway.

Air traffic controller Brian Delucchi said the flight path of the plane looked “extremely strange,” and he ordered the plane to go around.

Regulators found pilot error in three of the five close-calls involving aircraft reported in the past 16 months at the airport.

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9:05 a.m.

Federal authorities have determined most of the close-calls reported since December 2016 at the busy San Francisco International Airport were caused by pilots.

The East Bay Times reports Wednesday the Federal Aviation Administration found that three instances planes lined up for wrong runways and taxiways due to pilot error.

A fourth plane was mistakenly cleared to land in the wrong runway by a tower controller.

The airport has been under more scrutiny since a July 8 incident involving an Air Canada plane that nearly landed on an SFO taxiway crowded with four fully loaded aircraft.

That investigation led by the National Transportation Safety Board is ongoing.

Since then, the airport has buttressed its ground radar system and shut down a confusing taxiway.